Electrode



May 3, 1932. A. L. GODDARD ELEG TRODE Filed April 5. 1929 LZQvQWLZ. 6.126247%,

,UJQUM Patented May 3, 1932 UNITED STATES PATENT orrlcr.

ARTHUR L. GODDARD, OF CHICAGO, ILLINOIS, ASSIGNOR TO FLASHTBIG SIGN WORKS, A COPARTNERSHIP COMPOSED OF FRED PARKER AND HARRY S. YARKER, BOTH OF CHICAGO, ILLINOIS ELECTRODE Application filed April 5, 1929. Serial No. 352,648.

This invention relates to improvements in electrodes for lumlnescent gas discharge lamps and tubes such as are now employed for electric advertising and display signs.

In the operation of these tubes, the electrical discharge within the tubes results in the bombardment of the electrodes by the positive ions set free from the atoms of the ionized gas. Under this action, which is very violent, small particles'of the electrode material are shot with great force from the electrodes toward the surrounding wall of the outer glass tubes. To reduce the violence of this bombardment of the electrodes by the positi e ions, I surround the electrodes with tubular glass shields which .check the velocity of the approaching ions and reduce the excessive sputtering of the electrodes.

These shields, while they are supported in the outer glass tube out of contact with both the electrode and the tube wall are subject will be sufficiently removed from the outer end of the seal tube that the heat used in fusing the outer end of the seal tube to the outer tube will not crack or otherwise afiect the junction between them.

With relatively small electrodes, such as -ones having an area not exceeding 1.5 square decimeters per ampere, the bombardment is distributed over the entire area of the electrodes due to the small size thereof, and with the electrodes close to or in contact with the seal tube at its inner end, the heat caused by the bombardment is conducted to the seal tube. Withthe latter relatively long and having its tubular body open to the atmosphere at the outer end of the tube, such heat may radiate to the atmosphere and be carried ofi fast enough so that theseal'tube will not be heated sufiicientlyto causecracking of the juncture of the seal tube with the shield or with the outer tube. Thus with my to considerable heating first, from the elecinvention, the cracking hazard at the electrodes which become hot from the bombardtrode ends of discharge tubes due to heat with ment above referred to and second from the small electrodes is minimized and the life of hot sputtered material deposited on them from the electrodes. The supports for these shields are usually in the form of sealitubes which extend into the outer tubes. The seal tubes also support the electrodes and provide the vacuum seals for the outer tubes.

the seal tube so that there are no unequal sections in the shield wall to expand and contract diiferently and thus break or crack the shield particularly at the junction with the seal tube.

' Another object of my invention is to make the shield larger in diameter than the seal tube so that the shieldmay extend over the seal tube and be oined therewith at a pointsufficiently removed from the electrode that the heat produced at the same during the formation of the tube and during its op'erationwill not crack or otherwise affect the junction between the shield and the seal tube.

A further object of my invention is to make the seal tube relatively long so that the junbtion between. the shield and the seal tube Fig. 2 is an enlarged longitudinal sectional view through the electrode end of oneof said tubes, taken on line 2-2 of Fig. 1; and i an electric display s. 'Fig. 3 shows the electrode unit before be-' ,ing inserted in the outer tube. In the drawings 1, 1 nescentgas discharge tube characters of the sign, and 2 indicates thefsign body on the outer side of which said tube characters are.

mounted and supported for display; Each tube character 1 consists of a single length of appropriate glass tubing. bent to the shape desired and having enlarged and elongated (bulb-like end portions ,3 at the opposite ends of the tube. The bulbs 3'are usually dlsposed at right to the of the tube and ex tend into the bodv through. openings 4.

therein, as shown Fig. 2.

' dicate the lumi- Located in each bulb portion 3 is an electrode element 5 in the form of a relatively short piece or section of metal or other desired material through which the electric current is discharged into the tube 1 to ionize the gas confined therein. The gas employed may be neon or any other of the rare gases of thenoble gas group which are used in these tubes for illuminating purposes.

The bulb portions 3 of each tube are sealed so that a low vacuum may be produced in the tube as required for tubes of this character. The seal at each end of a tube is made through the use of a seal tube 6 which is made separate from the tube and afterwards inserted therein in the preparation of the tube. (See Fig. 3.) The seal tube 6 has a diameter less than the bulb portion 3 so that the seal tube may be inserted therein. The seal tube is also made of glass of the same character as the outer tube 1 and the two are connected together by fusing at the outer end a of the seal tube. The inner end of the seal tube 6 is closed by fusing to provide the vacuum seal 7 for the outer tube. Electric current for the .electrodeelement 5 is carried thereto by the lead-in wire 8 which is sealed in the seal 7 and extends to and is connected with the element 5 and supports the same at the inner end of the seaftube 6 as shown in Fig. 2. The wire 8 may be looped at the element 5 to better support the same.

Located in the bulb portion 3 about the element 5 is a tubular shield 9 made of glass of the character required and having a diameter larger than the element 5 and the seal tube 6 so that the shield may fit about both of the same. The shield 9 extends over the seal tube 6 to a point well beyond the seal 7 and is joined to the seal tube by fusing the two together beyond the seal. The tubular body of the seal tube 6 is made relatively long, as shown in Figs. 2 and 3, so that the junction of the shield 9 with the seal tube is removed far enough from the outer end a of the seal tube that the heat used in fusing the outer end of the seal tube to the outer tube 1 when preparing the tube will not crackthe junction between the two. This is an important feature of my invention'because it lessens the cracking hazard of the shields when joining the seal tube to the outer tube-in the, preparation of the latter.

In joining the shield 9 to the seal tube 6 beyond the seal 7, the junction of the two is far enough removed from the vicinity of the seal that the heat used in fusing the shield to the seal tube will not strain the previously made seal 7 and crack it as frequently happens when the shield is joined directly to the seal. This is another important feature of my invention because it lessens the cracking hazard of the vacuum seals when fusing the shieldtube to its support.

With the'seal tube 6 made relatively long,

as shown in the drawings, the electrode element 5 is far enough removed from the outer end of the seal tube that the heat generated at the element in the operation of the same Will not crack the junction between the seal tube and the outer tube because the heat has a chance to escape through the long wall of the seal tube to the atmosphere through the open outer end of the seal tube before reaching the junction between the seal tube. This is another important feature ofmy invention because it lessens the cracking hazard of the tubes whenrelativelysmallelectrodes areused, which electrodes due to their small size have the bombardment distributed entirely over them and thus generate much more heat than the so-called large electrodes.

The wall of the shield 9 has a substantially uniform thickness throughout the length of the shield sothat there are no unequal sections in the shield wall to expand and contract differently and break or crack the shield. A bulb is blown in the seal tube 6'beyond seal 7 so that the glass wall of the shield 9 may be kept substantially uniform to the very base of the shield and thus avoid unequal sections in the shield wall which by their diflerent rates of expansion and contraction would place unequal strains on the shield to crack it at its juncture with the seal tube. This is another important feature of my invention because it prevents cracking of the shields and exposing the electrodes to excessive bombardment. The shield projects beyond the inner end of the electrode 5 and protects it from excessive bombardment by checking the approach of the positive ions to the electrode 5.

My invention is particularly usable with small electrode elements of the size heretofore referred to as the heat generated at said electrodes is prevented from cracking the seals to put out the tubes. The leakage hazard with small electrodes is-thus greatly minimized and the tubes given long life.

The details of structure and arrangement of parts may be variously changed and modified without departing from the spirit and scope of my invention.

I claim as my invention:

An electrode unit for luminescent gas discharge lamps, comprising a reentrant seal tube closed at its inner end to provide a seal, an electrode element at said seal, a lead-in wire sealed in said seal and connected to said element, and an open ended tubular glass shield surrounding the element and the seal and joined to the tube beyond said seal, said tube having a bulb blown therein beyond the seal so that the shield may be joined thereto with its wall'maintained substantially uniform in. thickness at its junction with the tube. Tn testimony whereof Iafiix my signature.

ARTHUR 'L. GODDARD: 

